Grid does not automatically save and restore state. What am I doing wrong?

Grid does not automatically save and restore state. What am I doing wrong?

I have an Ext 3.4 grid with stateful:true, a stateId, and each column in the column model has an id.
Yet when I resize columns I don't see any state cookie saved, and the column widths are not restored when the page is reloaded.
I do have a state Manager with cookie provider defined and I can set/get cookie values via the state manager just fine.
I also added handlers for beforestatesave and statesave and they are being called, but still - no cookie is saved and no state restored. Those handlers are being passed the correct arguments as well - the columns argument show correct updated widths when dumped into the console.
My question is: am I doing something wrong? Should I not expect this to be automatic?
Do I actually have to use those state events to manually save and restore state?